Method for the purification of natural vanillin

ABSTRACT

The invention relates to a natural vanillin, which is in the form of an amorphous solid of which the color, in ethanolic solution at 10% by weight, is less than or equal to 200 Hazen, preferably less than or equal to 100 Hazen.

The present invention relates to a process for purifying naturalvanillin. The invention also relates to the natural vanillin that can beobtained by means of the process according to the invention and to afacility for producing purified natural vanillin.

Vanillin can be obtained via two distinct routes:

a “natural” route based on a biotechnological process, comprising inparticular the culturing of a microorganism (fungi, bacteria, etc.)capable of enabling the bioconversion of a fermentation substrate intovanillin. Such a process in which the fermentation substrate is ferulicacid is in particular known from EP 0 885 968 and EP 0 781 817. Thisprocess results in the production of a vanillin termed natural vanillin;

a “synthetic” route comprising conventional chemical reactions startingfrom guaiacol, not involving a microorganism. This process results inthe production of a vanillin termed synthetic vanillin.

Currently, natural vanillin, obtained via the “natural” route, ispurified by extraction with a solvent, followed by crystallization. Thisprocess results in a vanillin at specification limit: medium purity,colored, and at a yield of about 90%. The crystallization step has thedrawback of requiring the use of organic solvents. The use of suchsolvents, although authorized, can present drawbacks from atoxicological and/or environmental point of view.

As it happens, currently, no one is capable of providing a process forpurifying natural vanillin which does not require the use ofcrystallization organic solvent.

Processes for purifying synthetic vanillin by distillation are known.However, the streams at the end of the process for producing vanillinvia the natural route or via the synthetic route are quite distinct. Thestream at the output of the process for preparing natural vanillintypically comprises natural vanillin, vanillyl alcohol and a solvent,preferably a food-grade solvent, for example ethyl acetate. This streammay also comprise vanillic acid, ferulic acid, guaiacol, benzoic acid,dimers and trimers, guaiacol derivatives and water. The stream at theoutput of the process for preparing synthetic vanillin typicallycomprises synthetic vanillin, ortho-vanillin, trimers, guaiacol and DFG(diformaldehyde guaiacol). The way in which these various streams areapprehended is therefore distinct.

One objective of the present invention is therefore to provide a processfor purifying natural vanillin, in particular not requiring the use ofsolvent.

Another objective of the present invention is to provide a process forpurifying natural vanillin which is simple to carry out and which can becarried out continuously so as to be compatible with industrialprocesses. In particular, the present invention seeks the provision of aprocess for purifying natural vanillin which results in a yield greaterthan 90%, preferably greater than 95%.

Yet another objective of the present invention is to provide anadjustable process for purifying natural vanillin which makes itpossible to obtain, according to the desired specifications:

a very pure natural vanillin, for example having a purity greater orequal to 99%; or

a natural vanillin of lower purity, for example having a purity of 96%to 98.9%, and having, by virtue of the presence of certain impurities,organoleptic properties different than those of the very pure naturalvanillin and which are close to the organoleptic properties of vanillapod. The process according to the invention therefore advantageouslymakes it possible to control the level of residual impurities and inparticular those which have a positive influence on the organolepticquality of the final natural vanillin.

Since natural vanillin is a heat-sensitive product (in particularformation of trimers by heating vanillin), another objective of thepresent invention is to provide a purification process which preservesall the properties of vanillin.

It would also be advantageous to provide a process for purifying naturalvanillin which is more environmentally friendly and which makes itpossible to obtain a very pure and very weakly colored natural vanillinwithout degradation of its properties.

Yet other objectives will become apparent on reading the description ofthe invention that follows.

The natural vanillin according to the invention, and obtained by meansof the process of the invention, is a natural flavoring substanceaccording to article 9.2.c) of EC regulation 1334/2008. That is to sayit is a flavoring substance obtained by physical, enzymatic ormicrobiological processes from materials of plant, animal ormicrobiological origin taken as they are or after conversion thereof forhuman consumption by one or more of the conventional processes forpreparing food products. A natural flavoring substance corresponds to asubstance which is naturally present and has been identified in thenatural environment.

The invention therefore relates to a process for purifying naturalvanillin, comprising at least one step in which natural vanillin isevaporated.

The applicant has discovered, surprisingly, that a novel process forpurifying natural vanillin makes it possible to obtain a product havinga purity greater than or equal to 99% by weight and having a color lessthan or equal to 200 Hazen in ethanol solution at 10% by weight.

This process makes it possible, in particular when it is applied to astarting natural vanillin having a degree of purity ranging from 95% to99% by weight, to obtain a very weakly colored vanillin with a yieldgreater than or equal to 95% by weight relative to the initial amount ofvanillin present in the starting product.

In the context of the present invention, the term “process for producingnatural vanillin” is intended to mean processes for preparing vanillinvia biotechnological routes. Such processes comprise in particular theculturing of a microorganism capable of enabling the bioconversion of afermentation substrate into vanillin. Such a process in which thefermentation substrate is ferulic acid is M particular known from EP 0885 968 and EP 0 761 817.

In the context of the present invention, the term “natural vanillin” isintended to mean the vanillin obtained by means of preparation processesas defined above.

In the context of the present invention, the term “ultralightimpurities” or “ultralights” is intended to mean compounds of which thevolatility is higher than that of natural vanillin under the pressureand temperature conditions under consideration. The ratio between thevapor pressure of the ultralights and the vapor pressure of vanillin isbetween 60 and 200 at 134° C. (or at the distillation temperature).Among the ultralight impurities, mention may be made of ethyl acetate.

The term “light impurities” or “lights” is intended to mean compounds ofwhich the relative volatility is intermediate between that of theultralights and that of natural vanillin under the pressure andtemperature conditions under consideration. Among the light impurities,mention may be made of benzoic add and guaiacol.

The term “heavy impurities” or “heavies” is intended to mean compoundsof which the relative volatility is lower than that of natural vanillinunder the pressure and temperature conditions under consideration. Theratio between the vapor pressure of the heavies and the vapor pressureof vanillin is between 0.3 and 0.7 at 150°C. (or at the distillationtemperature). Among the heavy impurities, mention may be made of dimersand trimers of vanillin (i.e. compounds with a backbone having two,respectively three, phenyl groups, the dimers being advantageouslyselected from diphenylmethanes), vanillyl alcohol, vanillic acid,ferulic acid, benzoates, in particular sodium benzoate, and guaiacolderivatives, for example 4-methyl guaiacol and 4-ethyl guaiacol.

Generally, the volatility is the capacity of a substance to vaporize.

In a first aspect, the present invention relates to a process forpurifying a stream resulting from a process for producing naturalvanillin, said stream comprising natural vanillin and at least vanillylalcohol, by distillation enabling the separation of the natural vanillinfrom the vanillyl alcohol.

At the end of the process for preparing natural vanillin, a liquidstream (F1) comprising the natural vanillin, the ultralights, the lightsand the heavies is obtained. In one particular embodiment, theultralights represent from 50% to 90% by weight of the stream (F1), thelights represent from 0.1% to 10% by weight of the stream (F1), theheavies represent from 0.1% to 15% by weight of the stream (F1), and thenatural vanillin represents from 5% to 35% by weight of the stream (F1).Preferably, the ultralights represent from 60% to 80% by weight of thestream (F1), the lights represent from 0.5% to 5% by weight of thestream (F1), the heavies represent from 1% to 10% by weight of thestream (F1), and the natural vanillin represents from 10% to 30% byweight of the stream (F1).

The starting composition of the stream (F1) is given by way ofindication, and the process of the invention is also suitable formixtures comprising more or less natural vanillin.

In one particular embodiment, the stream (F1) comprises:

from 5% to 35% by weight of natural vanillin, in particular from 10% to30% by weight;

from 0.05% to 10% by weight of vanillyl alcohol, in particular from 0.1%to 5% by weight;

from 0.0% to 2% by weight of vanillic acid, in particular from 0.01% to0.6% by weight;

from 0.0% to 2% by weight of ferulic acid, in particular from 0.01% to0.9% by weight;

from 0.0% to 2% by weight of guaiacol, in particular from 0.01% to 0.6%by weight;

from 0.0% to 5% by weight of dimers and of trimers, preferably from0.05% to 5% by weight of dinners and of trimers, in particular from 0.1%to 5% by weight; the dimers and trimers being compounds with a backbonehaving respectively two or three phenyl groups. the dimers beingadvantageously selected from diphenylmethanes;

from 0.0% to 5% by weight of various organic compounds likewisebiosynthesized (for instance 4-methyl guaiacol, 4-ethyl guaiacol and/or4-vinyl guaiacol), preferably from 0.01% to 5% by weight, in particularfrom 0.05% to 1% by weight;

from 0.0% to 10% by weight of benzoic acid, preferably from 0.01% to 10%by weight of benzoic acid, in particular from 0.05% to 5% by weight;

from 0.0% to 5% by weight of water, preferably from 0.01% to 5% byweight of water, in particular from 0.05% to 3% by weight;

the remainder to 100% by weight being a food-grade solvent, for exampleethyl acetate.

Preferably, the operating pressure during distillation is between 2 and10 mbar, preferably between 3 and 6 mbar; for example it is 4 mbar.

In the context of the present invention, the term “operating pressure”is intended to mean the pressure at the top of the distillation column.

Advantageously, the pressure drop in the distillation column must be assmall as possible. Preferably, the pressure drop is between 1 and 10mbar, preferably between 2 and 8 mbar; for example it is 3 or 4 mbar.

In the context of the present invention, and unless otherwise indicated,the expression “between x and y” includes the values x and y. In thecontext of the invention, this expression also means “from x to y”.

In the process according to the invention, one or more distillationcolumns are used.

Preferably, the distillation column(s) comprise(s) from 7 to 40theoretical plates, preferably from 12 to 30 theoretical plates.

Advantageously, the process according to the invention makes it possibleto obtain a natural vanillin having a purity greater than or equal to96%, preferably greater than or equal to 98%.

In one embodiment, the process according to the invention makes itpossible to obtain a very pure natural vanillin, in particular having apurity greater than or equal to 99% and preferably containing less than1000 ppm of vanillyl alcohol. This embodiment can be obtained byadjusting the distillation parameters.

In another embodiment, the process according to the invention makes itpossible to obtain a natural vanillin of lower purity, for examplehaving a purity of 96% to 98.9% and comprising impurities which give thestream of natural vanillin obtained organoleptic properties which aredifferent than those of the very pure natural vanillin and close tothose of the vanilla pod. In this embodiment, the final stream ofnatural vanillin may comprise up to 3% by weight of impurities. Amongthe impurities are, in the majority, vanillyl alcohol, and the dimersand/or trimers, in particular diphenylmethanes, which can represent upto 1% by weight of the stream, and in the minority, vanillic acid,guaiacol, benzoic acid and biosynthesized organic compounds, which mayeach be present at up to 500 ppm in the stream. This embodiment can beobtained by adjusting the distillation parameters.

In the context of the process of the invention, a vanillin trimerizationchemical reaction may occur, which affects the vanillin yield.

The process for purifying natural vanillin by distillation according tothe present invention can be carried out in a different manner:

by batch distillation;

by continuous distillation; or

by continuous distillation on a divided wail column (DWC).

Batch Distillation

In one embodiment, the process according to the invention is carried outby batch distillation. The process thus comprises various unitarydistillation operations making it possible to distinctly separate theultralights, the lights, the vanillin and the heavies.

In the batch process, the stream (F1) is charged to a distillationcolumn. The process makes it possible to recover:

in a first fraction, the ultralights;

in a second fraction, the lights which may optionally comprise naturalvanillin at a low concentration;

in a third fraction, the stream comprising the natural vanillin; and

in the distillation concentrate, the heavies which may optionallycomprise natural vanillin at a low concentration.

In this embodiment, the term “low concentration” is intended to mean aconcentration preferably of at most 10%, preferably of at most 5%, forexample of at most 3% by weight relative to the total weight of thefraction.

The first, second and third fractions can advantageously be recovered bycondensation using conventional devices known to those skilled in theart.

Those skilled in the art are perfectly capable of setting thedistillation parameters, such as in particular the column diameter, thecolumn height and the packing. The following will simply be mentioned.The size (in particular the diameter) of the distillation columnsdepends on the stream circulating and on the internal pressure. Theywill therefore be sized mainly according to the flow rate of mixture tobe treated. It will be specified that the column can be packed withoutdistinction with plates or with stacked or woven packing, as is fullyknown to those skilled in the art. Once the facility has beendetermined, those skilled in the art adjust the operating parameters ofthe column.

Preferably, the distillation column comprises from 7 to 30 theoreticalplates, preferably from 5 to 15 theoretical plates, for example 7 to 10theoretical plates.

Preferably, the packing of the column is a woven packing with a surfacearea of 400 to 600 m²/m³.

This distillation process makes it possible to obtain the naturalvanillin with a yield of 90% to 95%, preferably of 90% to 93%.

In one embodiment, the process according to the invention makes itpossible to obtain a very pure natural vanillin, in particular having apurity greater than or equal to 99% and preferably containing less than1000 ppm of vanillyl alcohol.

In another embodiment, the process according to the invention makes itpossible to obtain a natural vanillin of lower purity, for examplehaving a purity of 96% to 98.9% and comprising impurities which give thestream of natural vanillin obtained organoleptic properties which aredifferent than those of the very pure natural vanillin and close tothose of the vanilla pod. In this embodiment, the final stream ofnatural vanillin may comprise up to 3% by weight of impurities. Amongthe impurities are, in the majority, vanillyl alcohol, and the dialersand/or trimers, in particular diphenylmethanes, which can represent upto 1% by weight of the stream, and in the minority, vanillic acid,guaiacol, benzoic acid and biosynthesized organic compounds, which mayeach be present at up to 500 ppm in the stream.

Continuous Distillation

In one embodiment, the process according to the invention is carried outby continuous distillation.

Topping/Tailing

In one particular embodiment, the process carried out by continuousdistillation comprises the following steps:

a) in a first step, the stream (F1) is treated in order to remove theultralights (stream (F11)) that it contains and more particularly theethyl acetate; the resulting stream comprising the natural vanillin, thelights and the heavies is called stream (F2);

b) in a second step, the stream (F2) is fed into a first distillationcolumn, making it possible to recover, at the top of the distillation, astream (F12) comprising the lights and which may optionally comprise alow concentration of natural vanillin, and at the bottom of thedistillation, a stream (F13) comprising the natural vanillin and theheavies and which may optionally comprise a low concentration of lights;

c) the stream (F13) is continuously fed into a second distillationcolumn, making it possible to recover, at the top of the distillation, astream (F14) comprising the natural vanillin, and at the bottom of thedistillation, a stream (F15) comprising the heavies and optionally a lowconcentration of natural vanillin.

Those skilled in the art are perfectly capable of setting thedistillation parameters, such as in particular the column diameter, thecolumn height and the packing. The following will simply be mentioned.The size (in particular the diameter) of the distillation columnsdepends on the stream circulating and on the internal pressure. Theywill therefore be sized mainly according to the flow rate of mixture tobe treated. It will be specified that the column can be packed withoutdistinction with plates or with stacked or woven packing, as is fullyknown to those skilled in the art. Once the facility has beendetermined, those skilled in the art adjust the operating parameters ofthe column.

In this embodiment, the term “low concentration” is intended to mean aconcentration preferably of at most 5%, preferably of at most 3%, forexample of at most 2% by weight relative to the total weight of thefraction.

According to one preferred embodiment of the topping/tailing scheme, atleast one part of the stream (F15) is mixed with the stream (F14) so asto be able to vary the final composition of a stream of purified naturalvanillin.

Preferably, the stream (F12) at the top of the distillation in step b)comprises the lights, and in particular benzoic acid and guaiacol andoptionally a low concentration of natural vanillin.

Preferably, the distillation column of step b) comprises from 20 to 35theoretical plates, preferably from 23 to 30 theoretical plates. Thedistillation column of step b) comprises in particular from 8 to 15theoretical plates for the concentration section and from 12 to 20theoretical plates for the depletion section, preferably from 10 to 13theoretical plates for the concentration section and from 13 to 17theoretical plates for the depletion section,

The distillation column of step b) may be a distillation column equippedwith stacked packing with a height of from 2×2600 mm to 2×3000 mm (2600mm to 3000 mm for each of the concentration and depletion sections). Thepacking of the column is preferably woven packing owing to the very lowprocessing pressures.

In the column of step b), the operating pressure is preferably between 2mbar and 10 mbar, preferably between 3 mbar and 6 mbar. The pressuredrop is preferably from 1 to 10 mbar and preferably from 1 to 8 mbar.During step b), the reflux ratio is between 10 and 30, preferablybetween 15 and 25.

The reflux ratio is defined as the ratio of the flow rate of materialreinjected from the top of the column to the inside of the column (i.e.the reflux flow rate) to the flow rate actually exiting at the outlet ofthe top of the column.

The stream (F2) feed point is selected in a manner known to thoseskilled in the art; it is in particular selected in such a way as toavoid back-mixing. Preferably, the feed point is at the top of thedepletion section.

The ratio of the distillation flow rate (flow rate of the stream (F12))to the feed flow rate (flow rate of the stream (F2)) is preferably from0.05 to 0.5.

The reflux flow rate is preferably from 1.4 to 3 times the feed flowrate; for example, it is twice the feed flow rate.

Preferably, during step b), the temperature at the bottom of the columnis between 100° C. and 160° C., particular between 120° C. and 150° C.Preferably, during step b), the temperature at the top of the column isbetween 80° C. and 120° C., preferably between 90° C. and 110° C.

The residence time of the vanillin at the bottom of the column of stepb) is between 30 minutes and 5 hours; it is for example 3 hours.

The distillation is initiated by adjusting the flow rate of stream (F12)so as to maintain an approximate temperature of preferably from 100 to160° C. The temperature difference between the top (vapor temperature)and the bottom (temperature of the liquid) is preferably between 35 and45° C.

In order to perform the distillation of step b), heat can be supplied tothe bottom of the column in particular by a falling-film or scraped-filmboiler, by a shell-and-tube heat exchanger heated with steam or by aheat-transfer fluid, by means of heating coils fed with steam or by aheat-transfer fluid or by any other equivalent device, preferably by aheat-transfer fluid. Preferably, the energy for the distillation issupplied by a boiler of falling-film type, a forced-circulationshell-and-tube device or a themosiphon shell-and-tube device.

The stream (F13) at the bottom of the column at the end of step b) issent to the distillation column of step c), also called tailing column.

Preferably, the column of step c) comprises from 10 to 30 theoreticalplates, preferably from 15 to 25 theoretical plates. The distillationcolumn of step c) comprises in particular from 4 to 14 theoreticalplates for the depletion section and from 6 to 16 theoretical plates forthe concentration section.

Preferably, the column of step c) is equipped, for example, with wovenstacked packing. The point of entry of the stream (F13) is locatedbetween the fifth and the fifteenth theoretical plates starting from thebottom of the distillation column.

In the column of step c), the operating pressure is preferably between 2and 10 mbar, preferably between 3 and 6 mbar, for example 4 mbar. Thepressure drop is preferably from 1 to 10 mbar, preferably from 1 to 8mbar; for example it is 4 mbar. During step c), the reflux ratio isbetween 2 and 10, preferably between 2.5 and 6; it is for example 3.

The ratio of the distillation flow rate (flow rate of the stream (F14))to the feed flow rate (flow rate of the stream (F2) is preferably from0.5 to 0.95.

The reflux flow rate is preferably from 1.4 to 3 times the feed flowrate; for example, it is twice the feed flow rate.

Preferably:

the flow rate of the stream (F1) is from 150 to 220 kg/h;

the flow rate of the stream (F11) is from 100 to 180 kg/h;

the flow rate of the stream (F2) is from 40 to 55 kg/h;

the flow rate of the stream (F12) is from 3 to 6 kg/h;

the flow rate of the stream (F13) is from 34 to 52 kg/h;

the flow rate of the stream (F14) is from 20 to 60 kg/h.

Preferably, during step c), the temperature at the bottom of the columnis between 160° C. and 200° C., in particular between 170° C. and 190°C. Preferably, during step c), the temperature at the top of the columnis between 100° C. and 160° C., preferably between 110° C. and 140° C.

The residence time of the vanillin at the bottom of the column of stepc) is between 15 minutes and 15 hours, preferably between 30 minutes and15 hours, more preferably between 7 and 15 hours. in order to reducethis residence time to between 15 minutes and 8 hours and to limit thedegradation of the natural vanillin, which is heat-sensitive, it may beadvantageous to add a deadweight at the bottom of the column.Deadweights are well known to those skilled in the art; they may inparticular consist of glass beads.

In order to perform the distillation of step c), heat can be supplied tothe bottom of the column in particular by a falling-film or scraped-filmboiler, by a shell-and-tube heat exchanger heated with steam or by aheat-transfer fluid, by means of heating coils fed with steam or by aheat-transfer fluid or by any other equivalent device, preferably by aheat-transfer fluid. Preferably, the energy for the distillation issupplied by a forced-circulation shell-and-tube device or a scrapedexchanger.

In one embodiment, the process according to the invention makes itpossible to obtain a very pure natural vanillin, in particular having apurity greater than or equal to 99% and preferably containing less than1000 ppm of vanillyl alcohol. This embodiment can be obtained byadjusting the distillation parameters; in particular the ratio of thedistillation flow rate (F14) to the feed flow rate (F2) is thenpreferably between 0.67 and 0.734.

In another embodiment, the process according to the invention makes itpossible to obtain a natural vanillin of lower purity, for examplehaving a purity of 96% to 98.9% and comprising impurities which give thestream of natural vanillin obtained organoleptic properties which aredifferent than those of the very pure natural vanillin and close tothose of the vanilla pod. In this embodiment, the final stream ofnatural vanillin may comprise up to 3% by weight of impurities. Amongthe impurities are, in the majority, vanillyl alcohol, and the dimersand/or trimers, in particular diphenylmethanes, which can represent upto 1% by weight of the stream, and in the minority, vanillin acid,guaiacol, benzoic acid and biosynthesized organic compounds, which mayeach be present at up to 500 ppm in the stream. This embodiment can beobtained by adjusting the distillation parameters; in particular theratio of the distillation flow rate (F14) to the feed flow rate (F2) isthen preferably between 0.735 and 0.8.

The invention also relates to a device for implementing this process,comprising:

a first device (1) for separating the ultralights. in particular theethyl acetate, from a stream (F1) entering said first device, this firstdevice being in particular a falling-film exchanger or a jacketedreactor;

a means for connecting the first device to a first distillation column(2) for transferring the stream exiting the first device (F2) to theinput of said first column;

a first distillation column (2) for separating, on the one hand, thelights and, on the other hand, the natural vanillin and the heavies,said first column comprising an input of the stream (F2) originatingfrom the first device and an output at the top of the column comprisingthe lights (F12), and an output at the bottom of the column comprisingthe natural vanillin and the heavies (F13);

a means for connecting the first column to a second distillation column(3) for transferring the stream exiting at the bottom of the firstcolumn to the input of said second column;

a second distillation column (3) for separating, on the one hand, thenatural vanillin and, on the other hand, the heavies, said second columncomprising an input of a stream (F13) originating from the first columnand an output at the top of the column comprising the natural vanillin(F14), and an output at the bottom of the column comprising the heavies(F15).

The device may also contain a pump (4) for transferring the streamresulting from the first device to the first distillation column.

The device may also contain a condenser connected to one of the outputsof the first device making it possible to recover the ultralights and/ora condenser connected to the column top of the column (2) making itpossible to recover the lights and/or a condenser connected to the topof column (3) making it possible to recover the natural vanillin.

The characteristics regarding the first device and the distillationcolumns are specified above.

Tailing/Topping

In one particular embodiment, the process carried out by continuousdistillation comprises the following steps:

a) in a first step, the stream (F1) is treated in order to remove theultralights (stream (F11)) that it contains and more particularly theethyl acetate; the resulting stream comprising the natural vanillin, theheavies and the lights is called stream (F2);

b) in a second step, the stream (F2) is fed into a first distillationcolumn, making it possible to recover, at the top of the distillation, astream (F22) comprising the lights and and the natural vanillin andoptionally a low concentration of heavies, and at the bottom of thedistillation, a stream (F23) comprising the heavies, in particularvanillyl alcohol, and optionally a low concentration of naturalvanillin;

c) the stream (F22) is continuously fed into a second distillationcolumn, making it possible to recover, at the top of the distillation, astream (F24) comprising the lights and optionally a low concentration ofnatural vanillin, and at the bottom of the distillation, a stream (F25)comprising the natural vanillin and optionally a low concentration oflights and/or of heavies.

In this embodiment, the term “low concentration” is intended to mean aconcentration preferably of at most 10%, preferably of at most 5%, forexample of at most 3% by weight relative to the total weight of thefraction.

According to one preferred embodiment of the tailing/topping scheme, atleast one part of the stream (F23) is mixed with the stream (F25) so asto be able to vary the final composition of a stream of purified naturalvanillin.

Preferably, the stream (F22) at the top of the distillation in step b)comprises the lights, in particular benzoic acid and guaiacol, thenatural vanillin and optionally a low concentration of heavies. At thebottom of the distillation (F23) are the heavies, in particular thevanillyl alcohol, and optionally a low concentration of naturalvanillin.

Those skilled in the art are perfectly capable of setting thedistillation parameters, such as in particular the column diameter, thecolumn height and the packing. The following will simply be mentioned.The size (in particular the diameter) of the distillation columnsdepends on the stream circulating and on the internal pressure. Theywill therefore be sized mainly according to the flow rate of mixture tobe treated. It will be specified that the column can be packed withoutdistinction with plates or with stacked or woven packing, as is fullyknown to those skilled in the art. Once the facility has beendetermined, those skilled in the art adjust the operating parameters ofthe column.

Preferably, the column of step b) comprises from 10 to 30 theoreticalplates, preferably from 15 to 25 theoretical plates. The distillationcolumn of step b) comprises in particular from 4 to 14 theoreticalplates for the depletion section and from 6 to 16 theoretical plates forthe concentration section.

Preferably. the column of step b) is equipped, for example, with wovenstacked packing. The point of entry of the stream (F2) is locatedbetween the fifth and the fifteenth theoretical plates starting from thebottom.

In the column of step b), the operating pressure is preferably between 2and 10 mbar, preferably between 3 and 6 mbar, for example 4 mbar. Thepressure drop is preferably from 1 to 10 mbar, preferably from 1 to 8mbar; for example it is 4 mbar. During step b), the reflux ratio isbetween 2 and 10, preferably between 2.5 and 6; it is for example 3.

The ratio of the distillation flow rate (flow rate of the stream (F22))to the feed flow rate (flow rate of the stream (F2)) is preferably from0.5 to 0.95.

The reflux flow rate is preferably from 1.4 to 3 times the feed flowrate; for example, it is twice the feed flow rate.

Preferably, during step b), the temperature at the bottom of the columnis between 160° C. and 200° C., in particular between 170° C. and 190°C. Preferably, during step b), the temperature at the top of the columnis between 100° C. and 160° C., preferably between 110° C. and 140° C.

The residence time of the vanillin at the bottom of the column of stepb) is between 15 minutes and 15 hours, preferably between 30 minutes and15 hours, and even more preferably between 7 and 15 hours. In order toreduce this residence time to between 15 minutes and 8 hours and tolimit the degradation of the natural vanillin, which is heat-sensitive,it may be advantageous to add a deadweight at the bottom of the column.Deadweights are well known to those skilled in the art; they may inparticular consist of glass beads.

In order to perform the distillation of step b), heat can be supplied tothe bottom of the column in particular by a falling-film or scraped-filmboiler, by a shell-and-tube heat exchanger heated with steam or by aheat-transfer fluid, by means of heating coils fed with steam or by aheat-transfer fluid or by any other equivalent device, preferably by aheat-transfer fluid. Preferably, the energy for the distillation issupplied by a forced-circulation shell-and-tube device or a scrapedexchanger.

The stream (F22) at the top of the column at the end of step b) is sentto the distillation column of step c), also called topping column. Thisstream can be sent in liquid form, the vapors originating from thecolumn of step b) being totally condensed by means of a condenser, or invapor form, the vapors originating from the column of step b) beingpartially condensed by means of a partial condenser. Preferably, thestream (F22) is sent to the distillation column of step c) in the vaporphase. This advantageously enables a direct saving of live vapor for thedistillation column of step c). Thus, the operating pressure of thedistillation column of step b) must be greater than that of thedistillation column of step c) and a partial condenser is placed betweenthe distillation column of step b) and that of step c). The partialcondenser may be of any type of condenser known to those skilled in theart; it may for example be a condenser of shell-and-tube type.

Preferably, the stream (F24) at the top of the distillation in step c)comprises the lights, in particular benzoic acid and guaiacol, andoptionally natural vanillin at low concentration.

Preferably, the distillation column of step c) comprises from 20 to 35theoretical plates, preferably from 23 to 30 theoretical plates. Thedistillation column of step b) comprises in particular from 8 to 15theoretical plates for the concentration section and from 12 to 20theoretical plates for the depletion section, preferably from 10 to 13theoretical plates for the concentration section and from 13 to 17theoretical plates for the depletion section. The distillation column c)may be a distillation column equipped with stacked packing with a heightof from 2×2600 mm to 2×3000 mm (2600 to 3000 mm for each of theconcentration and depletion sections). The packing of the column ispreferably woven packing owing to the very low processing pressures.

In the column of step c), the operating pressure is preferably between 2and 10 mbar, preferably between 3 and 6 mbar, for example 4 mbar. Thepressure drop is preferably from 1 to 10 mbar, preferably from 1 to 8mbar; for example it is 4 mbar. During step c), the reflux ratio isbetween 10 and 30, preferably between 15 and 25; it is for example 20.The stream (F22) feed point is selected in a manner known to thoseskilled in the art, it is in particular selected in such a way as toavoid back-mixing. Preferably, the feed point is at the top of thedepletion section.

The ratio of the distillation flow rate (flow rate of the stream (F24))to the feed flow rate (flow rate of the stream (F2) is preferably from0.05 to 0.5.

The reflux flow rate is preferably from 1.4 to 3 times the feed flowrate; for example, it is twice the feed flow rate.

Preferably, during step c), the temperature at the bottom of the columnis between 100° C. and 160°C., in particular between 120° C. and 150° C.Preferably, during step c), the temperature at the top of the column isbetween 80° C. and 120° C., preferably between 90° C. and 110° C.

The residence time of the vanillin at the bottom of the column of stepa) is between 30 minutes and 5 hours; it is for example 3 hours.

The distillation is initiated by adjusting the flow rate of stream (F22)so as to maintain an approximate temperature of from 100 to 160° C. Thetemperature difference between the top (vapor temperature) and thebottom (temperature of the liquid) is between 35 and 45° C.

In order to perform the distillation of step a), heat can be supplied tothe bottom of the column in particular by a falling-film or scraped-filmboiler, by a shell-and-tube heat exchanger heated with steam or by aheat-transfer fluid, by means of heating coils fed with steam or by aheat-transfer fluid or by any other equivalent device, preferably by aheat-transfer fluid. Preferably, the energy for the distillation issupplied by a boiler of falling-film type, a forced-circulationshell-and-tube device or a themosiphon shell-and-tube device.

Preferably:

the flow rate of the stream (F1) is from 150 to 220 kg/h;

the flow rate of the stream (F11) is from 100 to 180 kg/h;

the flow rate of the stream (F2) is from 40 to 55 kg/h;

the flow rate of the stream (F22) is from 33 to 52 kg/h;

the flow rate of the stream (F23) is from 7 to 17 kg/h;

the flow rate of the stream (F25) is from 20 to 60 kg/h.

In one embodiment, the process according to the invention makes itpossible to obtain a very pure natural vanillin, in particular having apurity greater than or equal to 99% and preferably containing less than1000 ppm of vanillyl alcohol. This embodiment can be obtained byadjusting the distillation parameters; in particular the ratio of thedistillation flow rate (F24) to the feed flow rate (F2) is thenpreferably between 0.06 and 0.083.

In another embodiment, the process according to the invention makes itpossible to obtain a natural vanillin of lower purity, for examplehaving a purity of 96% to 98.9% and comprising impurities which give thestream of natural vanillin obtained organoleptic properties which aredifferent than those of the very pure natural vanillin and close tothose of the vanilla pod. In this embodiment, the final stream ofnatural vanillin may comprise up to 3% by weight of impurities. Amongthe impurities are, in the majority, vanillyl alcohol, and the dimersand/or trimers, in particular diphenylmethanes, which can represent upto 1% by weight of the stream, and in the minority, vanillic acid,guaiacol, benzoic acid and biosynthesized organic compounds, which mayeach be present at up to 500 ppm in the stream. This embodiment can beobtained by adjusting the distillation parameters; in particular theratio of the distillation flow rate (F24) to the feed flow rate (F2) isthen preferably between 0.084 and 0.1.

The invention also relates to a device for implementing this process,comprising:

a first device (1) for separating the ultralights, in particular theethyl acetate, from a stream (F1) entering said first device, this firstdevice being in particular a falling-film exchanger or a jacketedreactor;

a means for connecting the first device to a first distillation column(5) for transferring the stream (F2 exiting the first device to theinput of said first column;

a first distillation column (5) for separating, on the one hand, thelights and the vanillin and, on the other hand, the heavies, said firstcolumn comprising an input of the stream (F2) originating from the firstdevice and an output at the top of the column comprising the lights andthe natural vanillin (F22), and an output at the bottom of the columncomprising the heavies (F23);

a means for connecting the first column to a second distillation column(6) for transferring the stream (F22) exiting at the top of the firstcolumn to the input of the second column;

a second distillation column (6) for separating, on the one hand, thenatural vanillin and, on the other hand, the lights, said second columncomprising an input of a stream (F22) originating from the first columnand an output at the top of the column comprising the lights (F24), andan output at the bottom of the column comprising the natural vanillin(F25).

The device may also contain a pump (4) for transferring the streamresulting from the first device to the first distillation column.

The device may also contain a condenser connected to one of the outputsof the first device and making possible to recover the ultralightsand/or a condenser connected to the column top of the column (6) makingit possible to recover the lights.

in the case where the input stream of the second distillation column isintroduced in the vapor phase, the device also comprises a partialcondenser connecting the column top of the first column (5) and the feedpoint of the second column (6).

In the case where the input stream of the second distillation column isintroduced in the liquid phase. the device also comprises a condenserconnecting the column top of the first column (5) and the feed point ofthe second column (6).

The characteristics regarding the first device, the condenser and thedistillation columns are specified above.

The embodiment comprising the use of a partial condenser allowsconsiderable energy savings to be made, in particular in the context ofhigh production.

Continuous Distillation by Means of a Divided Wall Column (or DWC)

In one embodiment, the process according to the invention is carried outby continuous distillation using a divided wall column.

The process carried out by continuous distillation by means of a dividedwall column comprises the following steps:

a) in a first step, the stream (F1) is treated in order to remove theultralights (stream (F11)) that it contains and more particularly theethyl acetate; the resulting stream thus obtained comprising the naturalvanillin, the lights and the heavies is called stream (F2);

b) in a second step, the stream (F2) is fed into a divided wall columnwhich makes it possible to recover, at the top of the column, a stream(F32) comprising the lights and optionally a low concentration ofnatural vanillin, and at the bottom of the column, a stream (F34)comprising the heavies, and in particular vanillyl alcohol, andoptionally a low concentration of natural vanillin, the vanillin beingrecovered in the form of a stream (F33) by drawing off via a sidestream,it being possible for this stream to optionally comprise a lowconcentration of lights and/or of heavies.

In this embodiment, the term “low concentration” is intended to mean aconcentration preferably of at most 10%, preferably of at most 5%, forexample of at most 3% by weight relative to the total weight of thefraction.

The drawing off via a sidestream can be carried out in the liquid phaseand/or in the vapor phase. This may be done via any method known tothose skilled in the art. For example:

in the liquid phase, a packing wad can be replaced with an overflowrecovery tank;

in the vapor phase, via a link with a side condenser, the vent pressureof which is in equilibrium with the top pressure.

Advantageously, the vapor-phase drawing off via a sidestream avoidsentraining the heavies in the stream of natural vanillin obtained.

Advantageously, the liquid-phase drawing off via a sidestream allowsenergy to be saved, since the removal of enthalpy is very much less thana vapor-phase drawing off.

The vapor-phase drawing off advantageously makes it possible to increasethe purity of the vanillin obtained. The liquid-phase drawing off makesit possible, for its part, advantageously to retain impurities in thestream of final natural vanillin, thus making it possible to obtaindifferent organoleptic properties.

Advantageously, the process according to the invention may comprise twosimultaneous drawing off procedures via a sidestream, one liquid-phasedrawing off via a sidestream and one vapor-phase drawing off via asidestream. This makes it possible, in a single distillation step, tocollect streams of natural vanillin having different purity andtherefore having different organoleptic properties.

In the context of the present invention, the term “divided wall column”is intended to mean a distillation column comprising a vertical internalseparation segment separating the column into two half-columns with ageometry and a volume independent of one another, a primary half-columnin which the feeding of the stream (F2) takes piece and a secondaryhalf-column in which the drawing off of the stream (F34) takes place,the two half-columns communicating with one another, the separationsegment not going from one end to the other of the column.

Preferably, the divided wall column is such that the primary half-columncomprises between 18 and 30 theoretical stages, preferably between 25and 30 theoretical stages, for example 27 theoretical stages, and thesecondary half-column comprises between 18 and 25 theoretical stages,preferably between 20 and 25 theoretical stages, for example 23theoretical stages. Preferably, the primary half-column comprises from10 to 20 theoretical stages for the depletion section and from 8 to 10theoretical stages for the concentration section. Preferably, thesecondary half-column comprises from 10 to 20 theoretical stages abovethe point of vapor-phase drawing off via a sidestream and from 10 to 15theoretical stages below the point of vapor-phase drawing off. Theliquid-phase drawing off is 1 to 4 plates below the vapor-phase drawingoff.

Preferably, the operating pressure of the divided wall column is between2 and 10 mbar, preferably between 3 and 6 mbar, for example 4 mbar. Thepressure drop must preferably be identical m each of the twohalf-columns forming the divided wall column; for this, the diameter ofeach half-column is adjusted. The pressure drop in each half-column is0.5 to 2.5 mbar.

The reflux ratio in each half-column of the divided wall column, whichmay be identical or different, is preferably between 2 and 10,preferably between 2.7 and 6.

Preferably, the feeding of the stream (F2) takes place between the tenthand the twentieth theoretical stages of the primary half-column, theplates being counted from bottom to top. The vanillin is drawn off via asidestream from the divided wall column, preferably between the fourthand the fifteenth theoretical stages of the secondary half-column, theplates being counted from bottom to top.

Preferably, the separation segment comprises an orifice which allows avanillin-enriched stream to pass from the primary half-column to thesecondary half-column. The orifice is preferably at least twotheoretical plates above the feed with respect to the primaryhalf-column; it is preferably between 2 and 5 plates above the feed, theplates being counted with respect to the primary half-column. The sizeof the orifice is determined so as to allow a vanillin-enriched andlight-poor stream to pass through; the size of the orifice can bedetermined by those skilled in the art. It is preferably from 5 to 20mm. for example from 8 to 15 mm, in particular approximately 10 mm, wideacross the width of the separation segment.

The residence time at the bottom of the column is preferably from 30minutes to 13 hours, for example 8 hours. In order to reduce thisresidence time to between 1 and 7 hours and to limit the degradation ofthe natural vanillin, which is heat-sensitive, it may be advantageous toadd a deadweight at the bottom of the column. Deadweights are well knownto those skilled in the art; they may in particular consist of glassbeads.

In order to perform the distillation, heat can be supplied to the bottomof the column in particular by a failing-film or scraped-film boiler, bya shell-and-tube heat exchanger heated with steam or by a heat-transferfluid, by means of heating coils fed with steam or by a heat-transferfluid or by any other equivalent device, preferably by a heat-transferfluid.

Preferably, the ratio of the flow rate of total drawing off via asidestream (vapor and/or liquid) to the flow rate of stream (F2) is from0.5 to 0.95.

Preferably:

the flow rate of the stream (F1) is from 150 to 220 kg/h;

the flow rate of the stream (F2) is from 40 to 70 kg/h;

the flow rate of the stream (F32) is from 3 to 7 kg/h;

the flow rate of the stream (F33) in the vapor phase is from 20 to 60kg/h.

When the column comprises a double vapor and liquid drawing off, theflow rate of the vapor stream is from 35 to 45 kg/h and the flow rate ofthe liquid stream is from 1.0 to 2.5 kg/h.

In one embodiment, the process according to the invention makes itpossible to obtain a very pure natural vanillin, in particular having apurity greater than or equal to 99% and preferably containing less than1000 ppm of vanillyl alcohol. This embodiment is obtained by drawing offthe natural vanillin in vapor form. The ratio of the distillation (F33)flow rate to the feed (F2) flow rate is then preferably between 0.5 and0.734.

In another embodiment, the process according to the invention makes itpossible to obtain a natural vanillin of lower purity, for examplehaving a purity of 96% to 98.9% and comprising impurities which give thestream of natural vain obtained organoleptic properties which aredifferent than those of the very pure natural vanillin and close tothose of the vanilla pod. In this embodiment, the final stream ofnatural vanillin may comprise up to 3% by weight of impurities. Amongthe impurities are, in the majority, vanillyl alcohol, and the dimersand/or trimers, in particular diphenylmethanes, which can represent upto 1% by weight of the stream, and in the minority, vanillic acid,guaiacol, benzoic acid and biosynthesized organic compounds, which mayeach be present at up to 500 ppm in the stream. The ratio of thedistillation (F33) flow rate to the feed (F2) flow rate is thenpreferably between 0.736 and 0.76.

The process of the invention also makes it possible to obtain, by meansof a single distillation step, very pure vanillin, having a puritygreater than or equal to 99%, and vanillin having a purity of 96% to98.9% by envisioning two drawing off procedures via a sidestream, onevapor-phase drawing off making it possible to obtain vanillin having apurity greater than 99%, and one liquid-phase drawing off making itpossible to recover vanillin having a purity of 96% to 98.9%.

The present invention also relates to a device for implementing thisprocess, comprising:

a first device (1) for separating the ultralights, in particular theethyl acetate, from a stream (F1) entering said first device, this firstdevice being in particular a falling-film exchanger or a jacketedreactor;

a means for connecting the first device to a divided wail distillationcolumn (7) for transferring the stream exiting the first device (F2) tothe input of said divided wall column;

a divided wall distillation column (7) for separating the lights, theheavies and the natural vanillin, said divided wall column comprising aninput of the stream (F2) originating from the first device and an outputat the top of the column comprising lights (F32), an output at thebottom of the column comprising the heavies, and one or two devices fordrawing off the natural vanillin via a sidestream (F33).

The device also contains a pump (4) for transferring the streamresulting from the first device to the divided wall column.

The divided wall column comprises an internal segment (8) separating thecolumn into two half-columns (71) and (72). The segment comprises anorifice (9) as described above.

The characteristics regarding the first device and the divided wallcolumn are specified above.

The process by means of a divided wall column is the preferred variantof the invention.

Generally, in the processes of the invention, step a) can be carried outfor example by means of a falling-film exchanger or a shelled reactor(or jacketed reactor), preferably a falling-film exchanger.

The term “falling-film evaporator” (also called wetting-film evaporator)is intended to mean an apparatus consisting of a generally cylindricalchamber comprising a bundle of vertical tubes, said tubes being heatedexternally by circulation of steam in said chamber. The stream (F1) isfed via the upper part and falls onto a distribution system for examplewith an overflow allowing good distribution of the liquid at the top ofthe tubes so as to form a liquid film of fine thickness, generally lessthan 1 mm, preferably between 0.3 and 0.5 mm.

During this pre-step, the operating pressure is preferably atmosphericpressure.

The surface area of the exchanger is preferably from 0.3 to 0.6 m² for afeed flow rate of approximately 200 kg/h. For a different flow rate,those skilled in the art are capable, by virtue of their generalknowledge, of determining the surface area of the exchanger.

The ultralights, in particular the ethyl acetate, can be recovered,using a condenser, for subsequent use.

At the bottom of the falling-film evaporator, a recovery pump makes itpossible to send the liquid stream (F2) recovered at the output to thedistillation column of step b), also called divided wall column. Thestream (F2) corresponds to the stream (F1) substantially or totally freeof ultralights. The stream (F2) may optionally contain traces ofultralights that will be trapped in the cold trap of the column of stepb).

In a second particular aspect, a subject of the invention is a processfor purifying natural vanillin having a purity ranging from 95% to 99%by weight, so as to obtain weakly colored natural vanillin, comprisingthe following steps:

(a) melting the natural vanillin;

(b) subjecting the molten vanillin derived from step (a) to a vacuumevaporation step;

(c) recovering a condensate of purified natural vanillin. In this secondparticular aspect, a natural vanillin having a purity ranging from 95%to 99% by weight, i.e. comprising from 95% to 99% by weight of naturalvanillin, is used. It may also typically comprise from 1% to 5% byweight of impurities comprising phenolic oligomers. Among the impuritiescomprising phenolic oligomers, mention may in particular be made ofvanillin dialers and trimers.

The natural vanillin used in the process according to the invention hastherefore generally been pre-purified in order to achieve the degree ofpurity of 95% to 99% by weight.

Such a purification may have been carried out by any known method whichmakes it possible to achieve such a degree of purity, starting from acrude natural vanillin, i.e. one directly derived from biosynthesis.Preferably, the vanillin has been pre-purified by distillation, inparticular as described above in the context of the first aspect of theprocess according to the invention. Where appropriate, an extractionwith organic solvent, optionally followed by precipitation orcrystallization of the natural vanillin, can be carried out in order toperform such a purification.

Preferably, the second aspect of the process according to the inventionuses a natural vanillin obtained by distillation of crude naturalvanillin derived from a biosynthesis process.

Preferably, this pre-purification step will have made it possible toremove, inter alia, compounds of which the volatility is higher thanthat of natural vanillin under the pressure and temperature conditionsunder consideration. These compounds, which are derived from processesfor preparing natural vanillin, may be, inter age, benzoic acid,vanillyl alcohol, guaiacol and a solvent, preferably a food-gradesolvent such as ethyl acetate.

The term “volatility” denotes, in a manner known per se, the capacity ofa substance to vaporize.

In the second aspect of the process according to the invention, thecrude natural vanillin directly derived from biosynthesis typicallycomprises:

natural vanillin in a proportion which can range from 5% to 35% byweight, in particular from 10% to 30% by weight;

vanillyl alcohol in a proportion which can range from 0.05% to 10% byweight, preferably from 0.1% to 5% by weight;

vanillic acid in a proportion which can range from 0% to 2% by weight,preferably from 0.01% to 0.6% by weight;

ferulic acid in a proportion which can range from 0% to 2% by weight,preferably from 0.01% to 0.9% by weight;

guaiacol in a proportion which can range from 0% to 2% by weight,preferably from 0.01% to 0.6% by weight;

dimers and trimers in a proportion which can range from 0% to 5% byweight, preferably from 0.05% to 5% by weight, more preferably from 0.1%to 5% by weight; the dimers and trimers being compounds with a backbonehaving respectively two or three phenyl groups, the dimers beingadvantageously selected from diphenylmethanes;

various organic compounds which have likewise been biosynthesized (forinstance 4-methyl guaiacol, 4-ethyl guaiacol and/or 4-vinyl guaiacol) ina proportion which can range from 0.0% to 5% by weight, preferably from0.01% to 5% by weight, more preferably from 0.05% to 1% by weight;

benzoic acid in a proportion which can range from 0% to 10% by weight,preferably from 0.01% to 10% by weight, more preferably from 0.05% to 5%by weight;

water in a proportion which can range from 0% to 5% by weight,preferably from 0.01% to 5% by weight, more preferably from 0.05% to 3%by weight;

the remainder to 100% by weight being a food-grade solvent, inparticular ethyl acetate.

In the second aspect of the process according to the invention, thebiosynthesis process from which the natural vanillin used in theinvention is derived preferably confers on this natural vanillinorganoleptic properties close to those of the vanilla pod.

Particularly preferably, the second aspect of the process according tothe invention uses a natural vanillin having a purity ranging from 96%to 98.9% by weight.

According to another characteristic of the invention, the second aspectof the process according to the invention comprises an additional step(d) consisting of the recovery of a residue comprising phenolicoligomers, such as those described above.

In one preferred embodiment of the second aspect of the processaccording to the invention, the natural vanillin is melted during step(a) at a temperature ranging from 70 to 110° C. and at atmosphericpressure, more preferentially at a temperature ranging from 75 to 100°C. and at atmospheric pressure.

In the second aspect of the process according to the invention, step (a)is advantageously carried out under an inert gas atmosphere, i.e. whichpreferably has an oxygen content of less than or equal to 1% by volume.Suitable inert gases are nitrogen and argon, and mixtures thereof.

According to another characteristic of the second aspect of the processaccording to the invention, evaporation step (b) is advantageouslycarried out at a pressure ranging from 1 to 10 mbar and at a temperatureranging from 110 to 160° C.

More preferably, evaporation step (b) is carried out at a pressureranging from 1 to 6 mbar. Equally preferably, evaporation step (b) iscarried out at a temperature ranging from 115 to 135° C.

According to one particularly advantageous embodiment of the secondaspect of the process according to the invention, step (b) of theinvention is carried out in an evaporator. Said evaporator may moreparticularly be selected from a scraped-film evaporator or afalling-film evaporator. Particularly preferably, step (b) is carriedout in a scraped-film evaporator.

Evaporators that can be used for this purpose are thus thin-filmevaporators such as falling-film or scraped-film evaporators. Suchevaporators are commercially available, from the companies Buss AG, GEACanzler or Kuhni, and are well known to those skilled in the art. In aparticularly preferred variant of the second aspect of the processaccording to the invention, a short-path scraped-film evaporator, theprinciple of which is based on a short passage time of the product to beevaporated, is used. The scraped-film evaporator has proved to beparticularly suitable for purification by evaporation of naturalvanillin, and makes it possible to avoid any degradation of thisheat-sensitive product.

The molten natural vanillin derived from step (a) is then introducedinto such an evaporator. A thin film of liquid phase, comprising thenatural vanillin, is evaporated on a heated surface and the liquid phasecomprising phenolic oligomers is scraped by a mechanical means of bladeor roll type. Said liquid phase may then be recovered in a dedicatedcontainer.

The evaporator makes it possible to recover a gas effluent containingthe evaporated vanillin, which is then condensed so as to recover thepurified vanillin.

Advantageously, the passage time of the natural vanillin in theevaporator is less than or equal to 15 minutes, preferably less than orequal to 10 minutes, more preferably less than or equal to 5 minutes.

According to one passage of the second aspect of the process accordingto the invention, the natural vanillin condensate recovered in step (c)has a purity greater than or equal to 99% by weight, preferably greaterthan or equal to 99.5% by weight.

Advantageously, the condensate of purified natural vanillin, obtained bymeans of the process according to the invention, in particular the firstor second particular aspect, is then directly formed by directsolidification, preferably by spalling, pelletizing or prilling(agglomeration).

One of the preferred techniques for forming the condensate of purifiednatural vanillin is the technique of spelling on a cylinder or on abelt.

In this technique, the condensate of purified natural vanillin isbrought into contact with a metal cylinder or belt at a temperature of50° C., and then, by scraping the solid film obtained on the cylinderwith a knife, the condensate is recovered in the form of flakes.

Another preferred technique is pelletizing, which consists of a processof agglomeration of solid particles by solidification on a pelletizingbelt cooled to 10° C. Thus, the condensate of purified natural vanillinis in the form of a dry amorphous solid.

Prilling is also a preferred forming technique. It is a technique wellknown to those skilled in the art, consisting in spraying the vanillincondensate into a stream of cold air or nitrogen so as to obtain solidbeads or agglomerates (grills).

The condensate of purified natural vanillin may also be refined bymilling or sieving. The milling operation in particular may be performedin a standard apparatus such as a paddle mill, a pin mill or agranulator.

The process according to the invention has the advantage of making itpossible to obtain a very weakly colored vanillin of very high purity(greater than 99% by weight).

In order to characterize the coloration of the vanillin obtained, it canbe dissolved in ethanol, at a concentration of 10% by weight.

Thus, the condensate of natural vanillin in ethanolic solution at 10% byweight has a color less than or equal to 200 Hazen, preferably less thanor equal to 100 Hazen. The color of the vanillin solution can inparticular be measured in accordance with ISO standard 6271 or ASTMstandard D1209. A Konica-Minolta CM-5 colorimeter can be used for thispurpose.

A subject of the invention is also the vanillin which can be obtained bymeans of the process according to the invention. Said vanillin is in theform of an amorphous solid of which the color, in ethanolic solution at10% by weight, is less than or equal to 200 Hazen, preferably less thanor equal to 100 Hazen.

FIG. 1 represents a diagram of continuous topping/tailing distillationof a stream of natural vanillin (F1).

FIG. 2 represents a diagram of continuous tailing/topping distillationof a stream of natural vanillin (F1).

FIG. 3 represents a diagram of continuous distillation in a divided wallcolumn of a stream of natural vanillin (F1).

The present invention is illustrated in a nonlimiting manner by thefollowing examples.

EXAMPLES

The following examples describe the distillation of a stream of vanillin(F1) comprising 20% by weight of natural vanillin; 4% by weight ofheavies (vanillic acid, vanillyl alcohol, ferulic acid, 4-methylguaiacol, 4-ethyl guaiacol, dimers and trimers, sodium benzoate); 0.5%by weight of water; 2.5% by weight of lights (benzoic add and guaiacol);73% by weight of ultralights (ethyl acetate).

Example 1 Distillation of the Stream (F1) by Batch Distillation

180 kg of the stream (F1) are fed into the boiler of a distillationcolumn, 700 mm in diameter, equipped with 10 theoretical plates, packedwith a woven packing having a surface area of 450 m²/m³. Theheat-transfer fluid is fixed at the beginning at 110° C. and the coolantis a Gilotherm oil at 20° C. The column is placed at total reflux for 3hours. A first fraction comprising ethyl acetate is thus recovered at aflow rate of 15 kg/hour with a reflux of 0.5 for 10 hours. The step ofremoving the acetate is ended when the operating pressure is 4 mbar fora heat-transfer fluid of 160° C.

A second fraction, comprising the lights and 10% by weight of vanillin,is then recovered at a flow rate of 2.4 kg/hour with a reflux ratio of100 for a period of 4 hours.

The column is again pieced at total reflux for 1 hour when thetemperature at the top of the column reaches 139° C.; for this, theheat-transfer fluid is regulated at 165° C.

A fraction of natural vanillin comprising the natural vanillin having apurity of 98.2% is then recovered at a flow rate of 6.1 kg/hour with areflux of 30 for a period of 10 hours. The operating pressure is 4 mbar.After 10 h, the distillate flow rate is reduced to 3 kg/hour and thereflux ratio is set at 100. The duration of this operation is 0.5 hour.The distillation is stopped when the temperature at the top reaches 143°C., the load remaining in the concentrate is approximately 9.6 kg andcomprises the heavies. The purification yield is equal to 93%.

Example 2 Distillation of the Stream (F1) by Continuous Topping/TailingDistillation

Example 2 refers to FIG. 1.

The stream (F1) is fed at a flow rate of 200 kg/hour at the top of afalling-film exchanger (1). This exchanger makes it possible to removethe ethyl acetate under a stream (F11) at a flow rate of 146 kg/hour.The stream (F11) is sent to a condenser (not represented) for recoveryof the ethyl acetate.

A stream (F2) is recovered at the output of the evaporator, whichcorresponds to the stream (F1) substantially free of ethyl acetate. Thetraces of ethyl acetate present in the stream (F2) are recovered in thecold trap of a distillation column (2), thus making it possible toprotect the column (2). The stream (F2) is sent to a (topping)distillation column (2) by means of a recovery pump (4), in partialrecycle mode, at a flow rate of 54 kg/hour. At the top of column (2), astream (F12) is recovered at a flow rate of 5 kg/hour, comprisingbenzoic acid, guaiacol and 3% by weight of vanillin. At the bottom ofcolumn (2), a stream (F13) is recovered which comprises the heavies andthe remaining natural vanillin which is sent to a tailing column (3) ata flow rate of 49 kg/hour. At the top of column (3), a stream (F14) ofnatural vanillin comprising 3% by weight of heavies, essentiallyconsisting of vanillyl alcohol and of dimers, including diphenylmethane,is recovered at a flow rate of 40 kg/hour. The purity of the vanillin isequal to 97%. The yield of the process is equal to 97%. At the bottom ofcolumn (3), a stream (F15) of the heavies and 3% by weight of naturalvanillin is recovered at a flow rate of 9 kg/hour.

The characteristics of the device are as follows:

Exchanger (1): Surface area m=0.5 m².

Column (2)

Equipped with (low-speed woven) stacked packing with a height of 2×2600mm 24 theoretical plates divided into 11 plates for the concentrationsection and 13 plates for the depletion section

Column 4 m in height

Operating pressure: 4 mbar

Reflux ratio: 20

The column is first classified for 5 h with a mixture of vanillin (90%by weight) and benzoic acid (10% by weight). The distillation is theninitiated by adjusting the flow rate of stream (F12) so as to maintainan approximate temperature of 140° C. The temperature difference betweenthe top (vapor temperature) and the bottom (temperature of the liquid)is 39.6° C. at 4 mbar. The column is in total reflux for theclassification phase.

The energy for the distillation is supplied by a boiler of falling-filmtype, a forced-circulation shell-and-tube device or a thermosiphonshell-and-tube device.

Column 3

Equipped with woven stacked packing having a surface area ofapproximately 450 m²/m³ with a height of 2×4560 mm

The feed point is at the mark Z=1500 mm

18 theoretical plates

Diameter of 600 mm

Operating pressure: 4 mbar

The column is placed in total reflux by means of a feedstock of purevanillin melted beforehand in an oven.

Reflux ratio: 3

Ratio [distillate flow rate]/[feed flow rate] is 0.808

The temperature difference between the top (vapor temperature) and thebottom (temperature of the liquid) is 43° C. at 4 mbar.

The energy for the distillation is supplied by a forced-circulationshell-and-tube device or a scraped exchanger. The pressure on the shellside is 16 bar.

Example 3 Distillation of the Stream (F1) by Continuous Tailing/ToppingDistillation Example 3 refers to FIG. 2.

The stream (F1) is fed at a flow rate of 198.26 kg/hour at the top of afalling-film exchanger (1). This exchanger makes it possible to removethe ethyl acetate under a stream (F11) at a flow rate of 147 kg/hour.The stream (F11) is sent to a condenser (not represented) for recoveryof the ethyl acetate.

A stream (F2) is recovered at the output of the evaporator, whichcorresponds to the stream (F1) substantially free of ethyl acetate. Thetraces of ethyl acetate present in the stream (F2) are recovered in thecold trap of a distillation column (5), thus making it possible toprotect the column (5). The stream (F2) is sent to a (tailing)distillation column (5) by means of a recovery pump (4), in partialrecycle mode, at a flow rate of 51.26 kg/hour. At the bottom of column(5), a stream (F23) comprising the heavies and 3% by weight of vanillinis recovered.

At the top of column (5), a stream (F22) comprising the lights, theremaining vanillin and 2.5% by weight of heavies is recovered at a flowrate of 44 kg/hour, and is sent to a topping column (6) at a flow rateof 44 kg/hour. At the top of column (6), a stream (F24) comprising thelights and 3% by weight of vanillin is recovered. At the bottom ofcolumn (6), a stream (F25) of natural vanillin comprising the vanillinand 2.5% by weight of heavies is recovered at a flow rate of 38.6kg/hour. The vanillin obtained has a purity of 99.9% and thepurification yield is 98.9%.

The characteristics of the device are as follows:

Exchanger (1): Surface area=0.5 m².

Column (5)

Equipped with woven stacked packing having a surface area ofapproximately 450 m²/m³ with a height of 2×4560 mm

The feed point is at the mark Z=1500 mm

18 theoretical plates

Diameter of 600 mm

Operating pressure: 4 mbar

Reflux ratio: 3

Ratio [distillate flow rate]/[feed flow rate] is 0.83

The reflux flow rate represents 2.49 times the feed flow rate

The temperature difference between the top (vapor temperature) and thebottom (temperature of the liquid) is 26° C. at 4 mbar.

The energy for the distillation is supplied by a forced-circulationshell-and-tube device or a scraped exchanger. The pressure on the shellside is 12 bar.

Column (6)

Equipped with (low-speed woven) stacked packing with a height of 2×2600mm

24 theoretical plates divided into 11 plates for the concentrationsection and 13 plates for the depletion section

Column 4 m in height

Operating pressure: 4 mbar

Reflux ratio: 20

The column is first classified for 5 h with a mixture of vanillin (90%by weight) and benzoic acid (10% by weight). The distillation is theninitiated by adjusting the flow rate of stream (F24) so as to maintainan approximate temperature of 140° C., The temperature differencebetween the top (vapor temperature) and the bottom (temperature of theliquid) is 35° C. at 4 mbar. The column is in total reflux for theclassification phase.

The energy for the distillation is supplied by a boiler of falling-filmtype, a forced-circulation shell-and-tube device or a themosiphonshell-and-tube device. The pressure on the shell side is 10 bar.

An alternative consists in feeding column (6) in the vapor phase:partial condensation via a partial condenser is used for this. Thisalternative is a direct saving of live vapor for column (6). Column (5)then operates at 5 mbar, column (6) remaining at 4 mbar. in this case,the temperature at the top displays 139° C. The partial condensercomprises an LIC regulating loop which controls the reflux flow rate.The total vapor flow rate arriving at the boiler is controlled byservo-control of the heat load to the boiler by the pressure drop of thecolumn (ΔP=3 mbar). The condenser is a horizontal shell-and-tube devicecomprising 80 tubes; of ND10 (ND: Nominal Diameter in mm) and of length1150 mm.

The coolant is a Gilotherm oil at 85°°C. and at a flow rate of 533 L/h.

The set liquid height of the LIC is 165 mm. This emergence makes itpossible to obtain 44 kg/h of efflux for 176 kg/h of vapor phase whichenters the condenser. The tared valve of the condenser vent is regulatedat 5 mbar (opening if >5 mbar). The flow rate of live vapor at the inputof column (6) is regulated so as to ensure a pressure drop of 3.3 mbar.

Example 4 Distillation of the Stream (F1) on a Divided Wall Column withVapor-Phase Drawing Off

Example 4 refers to FIG. 3.

The stream (F1) is fed at a flow rate of 200 kg/hour at the top of afalling-film exchanger (1). This exchanger makes it possible to removethe ethyl acetate under a stream (F11) at a flow rate of 147 kg/hour.The stream (F11) is sent to a condenser (not represented) for recoveryof the ethyl acetate.

A stream (F2) is recovered at the output of the evaporator, whichcorresponds to the stream (F1) substantially free of ethyl acetate. Thetraces of ethyl acetate present in the stream (F2) are recovered in thecold trap of a distillation column (7), thus making it possible toprotect the pump of the column. The stream (F2) is sent to adistillation column (7) at a flow rate of 53 kg/hour. The following arerecovered:

a stream (F32) comprising the lights and 3% by weight of vanillin at aflow rate of 5 kg/hour at the top of the column;

a stream (F33) by drawing off via a sidestream, comprising vanillin witha purity of 98.9% and 1.1% by weight of heavies essentially consistingof vanillyl alcohol at a flow rate of 39 kg/hour. The yield of thepurification process is equal to 96.5%;

a stream (F34) at the bottom of the column, comprising the heavies and3% by weight of vanillin at a flow rate of 8 kg/hour.

The characteristics of the device are as follows:

Exchanger (1): Surface area=0.5 m².

Column (7)

Divided wall column equipped with a dividing wall segment (8) delimitinga primary half-column (71) and a secondary half-column (72)

stacked packing with a specific surface area of 450 m²/m³ in the primaryhalf-column (71) with a height of 5410 mm and stacked packing in thesecondary half-column (72) with a height of 4560 mm

The primary half-column has 27 stages

The secondary half-column has 23 stages

Operating pressure: 4 mbar

Reflux ratio: 3 in each half-column.

A passage (9) in the segment (8) at the 3110 mm mark makes it possibleto enrich the concentration section of the 2nd half-column. The openingof the passage is a strip which does not exceed 10 mm in width.

A temperature difference between bottom and top of 74.9° C. when the toptemperature is around 116° C.

The reflux flow rate of the downstream section represents 2.18 times thefeed flow rate (F2) and that of the upstream section represents 25% ofthe feed flow rate (F2).

The set pressure drop is 1.3 mbar for the column.

The energy for the distillation is supplied by a boiler of scraped-filmtype, or a forced-circulation shell-and-tube device.

Example 5 Distillation of the Stream (F1) on a Divided Wall Column byVapor/Liquid Double Drawing Off

Example 5 refers to FIG. 3 to which an additional liquid drawing offpoint is added.

The stream (F1) is fed at a flow rate of 200 kg/hour at the top of afalling-film exchanger (1). This exchanger makes it possible to removethe ethyl acetate under a stream (F11) at a flow rate of 147 kg/hour.The stream (F11) is sent to a condenser for recovery of the ethylacetate.

A stream (F2) is recovered at the output of the evaporator, whichcorresponds to the stream (F1) substantially free of ethyl acetate. Thetraces of ethyl acetate present in the stream (F2) are recovered in thecold trap of a distillation column (7), thus making it possible toprotect the pump of the column. The stream (F2) is sent to adistillation column (7) at a flow rate of 53 kg/hour. The following arerecovered:

a stream (F32) comprising the lights and 3% by weight of vanillin at aflow rate of 5 kg/hour at the top of the column;

a stream (F33) by vapor-phase drawing off via a sidestream, comprisingvanillin with a purity of 99.8% and 0.2% by weight of heaviesessentially consisting of vanillyl alcohol at a flow rate of 38.2kg/hour;

a stream (F35) (not represented) by liquid-phase drawing off via asidestream, comprising vanillin with a purity of 98% and 2% by weight ofheavies at a flow rate of 1.7 kg/hour;

a stream (F34) at the bottom of the column, comprising the heavies and3% by weight of vanillin at a flow rate of 8 kg/hour.

The overall purification yield is 98.5%.

The characteristics of the device are as follows:

Exchanger (1): Surface area=0.5 m².

Column (7)

Divided wail column equipped with a dividing wall segment (8) delimitinga primary half-column (71) and a secondary half-column (72)

stacked packing with a specific surface area of 450 m²/m³ in the primaryhalf-column (71) with a height of 5410 mm and stacked packing in thesecondary half-column (72) with a height of 4560 mm

The primary half-column has 27 stages

The secondary half-column has 23 stages

Operating pressure: 4 mbar

Reflux ratio: 3 in each half-column.

A passage (9) in the segment (8) at the 3110 mm mark makes it possibleto enrich the concentration section of the 2nd half-column. The openingof the passage is a strip which does not exceed 10 mm in width.

The vapor-phase drawing off via a sidestream is located at 1200 mm withrespect to the base of the packing bed.

The liquid-phase drawing off via a sidestream is located 400 mm belowthe vapor-phase drawing off via a sidestream.

A temperature difference between bottom and top of 74.9° C. when the toptemperature is around 116° C.

The reflux flow rate of the downstream section represents 2.18 times thefeed flow rate (F2) and that of the upstream section represents 25% ofthe feed flow rate (F2).

The set pressure drop is 1.3 mbar for the column.

The energy for the distillation is supplied by a boiler of scraped-filmtype, or a forced-circulation shell-and-tube device.

Example 6 Purification in a Scraped-Film Evaporator (According to theInvention)

10 kg of natural vanillin, having a purity of 98.5% by weight and acoloration of approximately 5 Gardner (according to ASTM standard D1544)in ethanolic solution at 10% by weight, are melted in an oven, undernitrogen, at 95° C. and at atmospheric pressure. The molten naturalvanillin is then added to a thermostatted dropping funnel which feeds ashort-path scraped-film 0.05 m² evaporator (KDL-5 evaporator sold by thecompany UIC GmbH) at a temperature of 135° C. and at a pressure of 3mbar. The rotation speed of the evaporator is 200 revolutions/min andthe residence time of the vanillin in the evaporator is 45 seconds. Thefeed flow rate used is 500 g/h of molten natural vanillin,

The natural vanillin vapors are condensed at 100° C. on the internalcondenser of the scraped-film evaporator and the liquid condensate isdirected to a pelletizing belt cooled to 10° C. The residue comprisingphenolic oligomers is discharged into a residue container.

The pellets are recovered and then weighed.

At the end of the process according to the invention, 9.8 kg of purifiednatural vanillin are obtained, i.e. a yield of 98% by weight, having apurity greater than or equal to 99.5% by weight, and having a color (inethanolic solution at 10% by weight) equal to 60 Hazen (ISO standard6271).

Example 7 (Comparative)

The same batch of natural vanillin as in example 6, having a purity of98.5% by weight, was purified by recrystallization from a water/ethanolmixture (20/80 by weight).

At the end of the purification by recrystallization, purified naturalvanillin, having a degree of purity equal to 98.8% by weight, isobtained with a yield of 80% by weight. In ethanolic solution at 10% byweight, it has a coloration of 4 Gardner (according to ASTM standardD1544), i.e. much greater than 500 Hazen.

In fact, the process according to the invention makes it possible toobtain very pure natural vanillin, with a better yield, and especially amuch weaker coloration (much whiter vanillin).

1.-32. (canceled)
 33. A natural vanillin that is in the form of anamorphous solid of which the color, in ethanolic solution at 10% byweight, is less than or equal to 200 Hazen, preferably less than orequal to 100 Hazen.
 34. A natural vanillin according to claim 33 whichcan he obtained by means of a process comprising at least one step inwhich natural vanillin is evaporated.
 35. A natural vanillin accordingto claim 33 having a purity greater than or equal to 96%, preferablygreater than or equal to 98%, more preferably greater than or equal to99%.
 36. A natural vanillin according to claim 35 having a puritygreater than or equal to 99% and containing less than 1000 ppm ofvanillyl alcohol.
 37. A natural vanillin according to claim 35 having apurity of 96% to 98.9% and comprising up to 3% by weight of impurities.38. A natural vanillin according to claim 37 characterized byorganoleptic properties close to the organoleptic properties of vanillapod.
 39. A natural vanillin according claim 33 which is formed by directsolidification, preferably by spalling, pelletizing or grilling, morepreferably by spiting on a cylinder or on a belt.
 40. A natural vanillinaccording to claim 33 which is refined by milling or sieving.
 41. Anatural vanillin according to claim 34 having a purity greater than orequal to 96%, preferably greater than or equal to 98%, more preferablygreater than or equal to 99%.
 42. A natural vanillin according to claim41 having a purity greater than or equal to 99% and containing less than1000 ppm of vanillyl alcohol.
 43. A natural vanillin according to claim41 having a purity of 96% to 98.9% and comprising up to 3% by weight ofimpurities.
 44. A natural vanillin according to claim 43 characterizedby organoleptic properties close to the organoleptic properties ofvanilla pod.